Fix VDP removal at vcl.discard.

src/tests/arg.vtc

@@ -109,4 +109,5 @@ varnish v1 -vcl { backend b None; }
 # Tests oject finalization, freeing argv
 varnish v1 -cli "vcl.discard vcl1"
 varnish v1 -cli "vcl.discard vcl2"
+delay 1
 varnish v1 -cli "vcl.list"

src/tests/vdp.vtc

@@ -142,4 +142,6 @@ varnish v1 -vcl { backend b None; }
 
 # Tests the discard event, with removal of VDPs.
 varnish v1 -cli "vcl.discard vcl1"
+varnish v1 -cli "vcl.discard vcl2"
+delay 1
 varnish v1 -cli "vcl.list"

src/vdfp_pipe.c

@@ -479,12 +479,13 @@ vmod_event(VRT_CTX, struct vmod_priv *priv, enum vcl_event_e e)
 			if (map->vcl == ctx->vcl && map->vdp != NULL) {
 				VRT_RemoveVDP(ctx, map->vdp);
 				free(TRUST_ME(map->vdp));
+				map->vdp = NULL;
 				prev_map = map;
 			}
 			map = VRBT_NEXT(vdp_tree, &tree_h, map);
 			if (prev_map != NULL) {
-				VRBT_REMOVE(vdp_tree, &tree_h, map);
-				FREE_OBJ(map);
+				VRBT_REMOVE(vdp_tree, &tree_h, prev_map);
+				FREE_OBJ(prev_map);
 			}
 		}
 		return (0);